Pyrometer | Construction, Working and Types of Pyrometer

There are two types of Pyrometer.

1. Radiation pyrometer

2. Optical Pyrometer


1. Radiation pyrometer:

Radiation Pyrometer Diagram
Radiation Pyrometer

Principle of Radiation Pyrometer:

All bodies above absolute zero temperature radiate the heat. The amount of energy radiated by the body depends on the temperature of the body. This is called Stefan Boltzmann's law. 

This law can be used to measure the temperature of the body. Stefan Boltzmann's law is when applied to the non-black body takes the form.

W=OeT^4 or KT^4

where,  

           W= radient energy 

           O= stefan constant

           E= emissivity

           T= temperature of body

           K= constant


Stefan Boltzmann's law states that ''the amount of radiant energy emitted by the body is proportional to the fourth power of the absolute temperature.''


Construction and Working of Radiation Pyrometer:

The radiation pyrometer is designed to collect the radiation from the radiating object and focus it by means of mirrors or lens on a detector. 

The detector usually a thermocouple or thermopile produces emf proportional to the temperature and it is given to the suitable millivoltmeter. 

As the millivoltmeter is calibrated for temperature it shows the temperature of the body. The recorder attached with the thermopile also provides the graph of the temperature variation.

Thermopile and the lens are fitted in the blackened tube.


Advantages of Radiation Pyrometer:

1. Can measure very high temperature.

2. No direct contact with the object is required.

3. High speed of response.

4. Reasonable price.


Disadvantages of Radiation Pyrometer:

1. The scale is highly nonlinear.

2. Presence of smoke and dust particles in the vicinity may result in measurement errors.

3. Cooling is required to protect the instrument where the operating conditions are very hot.

4. The calibration depends on the emissivity of the target material.


Application of Radiation Pyrometer:

1. For high-temperature measurement above the limits of the thermocouple.

2. For measurement of temperature in the contaminated atmosphere.

3. For measurement of temperature where direct contact of the sensor is not possible.

4. Capable to measure the temperature of the moving or stationary objects.

5. For the temperature measurement of a large surface or object.


2. Optical Pyrometer:

Construction and Working Principle of Optical Pyrometer:

The optical pyrometer consists of a filament lamp. The radiation from the target surface is focused by an objective lens (L) upon the plane filament of an electric bulb. 

A red filter is placed between the eyepiece and the filament allows only a narrow band of wavelength to pass through it. 

The eyepiece is adjusted until the filament is in sharp focus. The filament is heated on passing a current through it by changing the value of the rheostat. 

As the current increases the temperature and the resistance of the filament increase. When the intensity of the radiation from a lamp is the same as the intensity of radiation from the target, the filament is indistinguishable. 

Three different conditions of the filament are also shown in fig. 

Optical Pyrometer
Optical Pyrometer


An ammeter connected in series with the filament measures the current passing through it may be calibrated to read the temperature of the filament and hence the temperature of the target.


Advantages of Optical Pyrometer:

  • Portable and simple in operation.
  • No direct contact with the object is required.
  • Capable to measure the temperature of the moving or stationary objects.
  • Can measure very high temperature.
  • Excellent accuracy.


Disadvantages of Optical Pyrometer:

  • Cannot measure the temperature of the pure gas flame because the flame of the pure gas is colorless.
  • Expensive
  • The probability of human errors is high because the operator has to adjust the current manually.
  • Because of manual adjustment, continuous measurement and automatic control of temperature are not possible.
  • Not suitable for temperature below 7000'c because the eye is insensitive to wavelength characteristics below this temperature.


Application of Optical Pyrometer:

  • Can measure very high temperature.
  • To check and calibrate the radiation pyrometer.
  • To measure the temperature of the moving or stationary object in steel and metal industries.
  • For measurement of temperature where direct contact of the sensor is not possible.
  • In steel and metal industries for measurement of high temperature in the refining and alloying processes.

FAQs:

1. What is Working principle is used in a pyrometer?

The basic principle of the pyrometer is, it measures the object's temperature by sensing the heat or radiation emitted from the object without making contact with the object. It records the temperature level depending upon the intensity of radiation emitted.

2. What is radiation pyrometer definition?

pyrometer measures the intensity of radiation from a body having an extremely high temperature.

3. What are the types of pyrometer?

Pyrometers can be broadly classified into two categories - optical pyrometers and infrared / radiation pyrometers.



Pyrometer | Construction, Working and Types of Pyrometer Pyrometer | Construction, Working and Types of Pyrometer Reviewed by Harish on April 21, 2021 Rating: 5

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